1. Field of the Invention
The present invention generally relates to optical transmit/receive modules and method of fabricating the same, and more particularly to an optical transmit/receive module which transmits and receives lights propagated through an optical fiber in two ways and a method of fabricating the same.
Nowadays, high-speed digital transmission services such as transmission services using an ISDN (Integrated Services Digital Network) and a CATV (CAble TeleVision) are available. It is expected that a demand of multimedia will explosively be raised at the beginning of the 21st century. Thus, the work of providing optical access networks (main networks) is in progress. In the future, an optical fiber will be extended up to an optical network unit (which functions as an optical subscriber line termination device) provided in a mast or the inside of a small-scale building, condominium or the like. Thus, optical signals are transmitted through the optical fiber in two ways so that high-speed broadband services can be presented. In order to realize such services, it is required to reduce the size and cost of the optical subscriber line termination device, which is implemented as an optical transmit/receive module.
2. Description of the Related Art
FIG. 1 illustrates a conventional optical subscriber line termination device (optical transmit/receive module) 70. The device 70 includes an optical module 71, an optical adapter 72, a fiber-fused-type WDM (Wavelength Division Multiplexing) filter 73, optical connectors 74 and 75, an optical cable 76, and optical fibers 77-79. The device includes a board on which optical components and electronic components are mounted. The optical module 71 has a laser diode LD for optical transmission and a photodiode PD for optical reception. The optical adapter 72 is used to detachably connect the optical fibers 77-79 for internal connections. The WDM filter 73 is of a fiber fusing type. The optical cable 76 connects the device to an optical transmission path.
A transmitted light having a wavelength xcex1 (=1.3 xcexcm) from the laser diode LD is applied to the WDM filter 73 via the optical adapter 72 and the optical fiber 78, and is also combined with the optical path of the optical fiber 77. Then, the combined light is transmitted to the optical cable 76 via the optical connector 75. A received light having a wavelength xcex2 (=1.55 xcexcm) from the optical cable 76 is applied to the WDM filter 73 via the optical fiber 77, and is distributed to the optical path of the optical fiber 79. Then, the distributed light is applied to the photodiode PD via the optical adapter 72.
However, the WDM filter 73 is large in size and is expensive. In addition, the optical adapter 72 and the optical connector 74 are needed to optically connect the WDM filter 73 of the fiber fusing type and the optical module 71. Hence, the conventional optical subscriber line termination device needs an increased number of components. Further, it is necessary to ensure a mounting radius of curvature greater than a threshold level in order to reduce loss caused in the optical fibers 77-79. Hence, the device needs a large mounting space and it takes a long time to mount the optical fibers 77-79.
It is a general object of the present invention to provide an optical transmit/receive module in which the above disadvantages are eliminated.
A more specific object of the present invention is to provide a compact, simple, highly reliable optical transmit/receive module.
The above objects of the present invention are achieved by an optical module receiving light traveling through an optical fiber in two ways configured as follows. A coupler is provided in a case member and is attached to an end surface of a ferrule having the optical fiber. The coupler allows light of a first wavelength to pass therethrough along a first optical axis of the optical fiber and reflects light of a second wavelength so that reflected light travels along a second optical axis perpendicular to the first optical axis. A light emitting element is provided so as to be located on one of the first and second optical axes. A light receiving element is provided so as to be located on the other one of the first and second optical axes.
Another object of the present invention is to provide a ferrule assembly which makes it possible to provide a compact, simple, highly reliable optical transmit/receive module.
This object of the present invention is achieved by a ferrule assembly comprising: a ferrule in which an optical fiber is provided; and a coupler attached to an end surface of the ferrule, the coupler allowing light of a first wavelength to pass therethrough along a first optical axis of the optical fiber and reflecting light of a second wavelength so that reflected light travels along a second optical axis perpendicular to the first opUcal axis.
A further object of the present invention is to provide a method of fabricating a compact, simple, highly reliable optical transmit/receive module.
This object of the present invention is achieved by a method of fabricating an optical module comprising the steps of: assembling a case member, a coupler attached to an end surface of a ferrule having the optical fiber, a light emitting element and a light receiving element into the optical module, the coupler allowing light of a first wavelength to pass therethrough along a first optical axis of the optical fiber and reflecting light of a second wavelength so that reflected light travels along a second optical axis perpendicular to the first optical axis, the ferrule having a step portion formed on a part of an outer circumference portion of the ferrule, the step portion being perpendicular to the second optical axis; projecting a laser beam onto the step portion in a direction perpendicular to the first optical axis; and adjusting an angle of rotation of the ferrule by referring to the laser beam reflected by the step portion.